Conversion of information contained in a surface into an electrical signal can be achieved in a number of ways.
In one arrangement relative movement is effected between a spot of light and an information bearing surface and reflected light from the spot is focussed onto a photocell. As the spot moves over the surface so the reflected light level varies in relation to the information content and a varying electrical signal derived from the photocell comprises the electrical video signal.
In another arrangement an electron beam is scanned over a photoconductive surface onto which an image of the surface is focussed. The electron beam current varies with the light level at different points of the photoconductive surface and an electrical signal derived from these current variations comprises the electrical video signal.
In a further arrangement a narrow band of an illuminated information bearing surface is focussed onto a line of photoelectric elements, which are addressed in sequence and produce an electrical signal a parameter of which (such as amplitude) varies with the light level falling on the individual elements as the latter are scanned. By moving the lens and photoelectric elements relative to the illuminated surface, so the latter is scanned in a series of parallel bands, each of which is effectively "scanned" by the sequential addressing of the elements.
Other arrangements are possible, it being understood that the foregoing are only exemplary of the large number of different types of devices which can be used as a scanner.
Irrespective of the scanning employed it is usually a prerequisite that the information bearing surface to be scanned is flat and conventionally a flat support is provided on which a document can be laid out flat and where necessary, a transparent sheet such as a sheet of glass is laid over the document so as to maintain the latter flat. Alternatively the document may be laid face down on a window typically formed from a sheet of glass and if required a backing marker is laid over the document so as to maintain the latter flat in contact with the window.
Where the document to be copied is a book, the latter may be laid out flat with the page to be copied flattened for example against a window through which the page is to be viewed. However, it is found that the flattening of a book in this way can cause the binding of the book to be damaged. Where old and valuable books are to be scanned the result of opening the book out and flattening the page to be scanned can seriously damage the book and it is an object of the invention described in a copending application to provide a document scanner for scanning the pages of a book without damaging the binding of the book.
In that copending application a scanner is described which includes a camera within a wedge shaped housing which views the page to be scanned through a window in the housing.
It is an object of the present invention to provide a document scanner which will allow both pages of the book to be scanned without the need to lower the book and turn it around.